Resulting from organ retrieval, cold preservation and a period of warm ischemia during the surgery, ischemia-reperfusion injury (IRI) often leads to primary graft non-function, may predispose to late chronic rejection, and contributes to the shortage of donor organs available for transplantation. At present, there is no specific treatment available to prevent IRI in transplant recipients. Moreover, mechanisms of IR-induced tissue damage, and how clinically-relevant innate immune responses contribute to graft rejection represents one of the most challenging yet understudied problems in clinical liver transplantation. We have identified the role of intrinsic PACAP neuropeptide in maintaining hepatic homeostasis in a non-transplant model of hepatic warm IRI. We have shown that treatment with PACAP neuropeptide ameliorated liver IRI by depressing macrophage function in cAMP-PKA dependent manner. Our pilot data from an ongoing clinical study show that PACAP and its receptors are preferentially induced in human IRI-resistant liver transplants, as compared to those suffering from severe IR-damage. Here, we propose to analyze the function of distinct PACAP signaling pathways in a clinically relevant mouse model of prolonged hepatic cold ischemia followed by orthotopic liver transplantation (OLT). Hypothesis: PACAP-mediated cAMP-PKA signaling at the macrophage (innate immune arm) - hepatocyte (defensive arm) interface regulates pro-inflammatory (pathogenic) and cytoprotective (homeostatic) functions in OLTs subjected to IRI. Aim 1: To define the role of PACAP neuropeptide in innate immune function in liver IRI. Hypothesis: PACAP inhibits TLR4 macrophage activation and promotes immune homeostasis in IR-stressed OLTs. Aim 2: To evaluate the role of PACAP neuropeptide in hepatoprotection in liver IRI. Hypothesis: PACAP enhances parenchyma cell autophagy and promotes hepatocyte survival. By identifying a novel PACAP mediated-neural regulation in the milieu of IR-stressed OLTs, this proposal puts forth the advances in hepatic immune modulation in a completely new context of innate immunity and parenchyma cytoprotection. Based on our preliminary experimental data, supported by clinical observations, findings from this exploratory proposal may have far reaching basic and practical ramifications, as taming of IR-triggered innate inflammation at the graft site is now considered critical for improving both short and long-term transplantation outcomes.